Recent developments in macromolecular architecture have led to progress in dendritic macromolecules including dendrimers and hyperbranched structures. These highly branched macromolecules are characterized by their non-linear structure, which prevents crystallization, and minimizes chain entanglements.
As a result, these macromolecules display an unusual viscosity profile and solubility behavior, when compared to high molecular weight typical linear polymers. Furthermore, unlike linear polymers, the number of functional end-groups in these highly branch macromolecules is directly proportional to their molecular weight.
Thus, the potential for high numbers of functional groups, and the overall globular nature of these types of materials are advantageous in applications related to surface activity, adhesion, rheology control, and cure.
Hyperbranched polymers, however, differ from dendrimers in their synthetic approach, and in the degree of regularity in their structure. As a result, hyperbranched polymers are much easier to make, but their molecular weight distribution at higher molecular weights approaches infinity, compared to dendrimers, which are made tediously one generation at a time, and often with several protection and unprotection steps, extensive purification steps; but the results are a molecular weight distribution close to unity.
Thus, hyperbranched polymers are more cost effective, and therefore are more suitable on a larger scale for most commercial applications.
All synthetic approaches to hyperbranched polymer up until now have been based on a divergent method, wherein a monomer having precisely two types of functional groups react one with the other, but do not react with themselves, and having an overall functionality that is greater than two. Most simple suitable monomers of this type contain a single A functional group and two B functional groups, i.e., an AB.sub.2 type monomer.
Such a divergent method is represented in FIG. 1 of the accompanying drawing. According to this scenario, if the monomer has a higher number of functional groups, a more dense structure is possible. Thus, a monomer containing a single A functional group and three B functional groups, i.e., an AB.sub.3 type monomer, it would lead to a higher branching density upon polymerization, and a higher concentration of the B functional group on the surface of the resulting polymer. In principle, therefore, AB.sub.X type polymers can be prepared wherein x can be any integer with a value greater than two.
Another key advantage of a hyperbranched polymer is the fact that the degree of branching can be controlled by increasing the free chain length between the functional groups. This alternative minimizes the crowding effect, and allows the production of higher molecular weight polymers.
Due to the large number of branches in such materials, the hydrodynamic volume of a hyperbranched polymer is smaller than that of a linear polymer of the same molar mass. This different relationship between the volume and molecular weight can be directly correlated with differences observed in viscosity, solubility, and other physical properties of hyperbranched polymers.
However, most hyperbranched polymers have been prepared by the polycondensation reaction of functional groups such as polyesters, ethers, and amides, with some hyperbranched polymers having been derived via C--C bonds. Some hyperbranched polymers have been prepared wherein a silane is used as a protective group during preparation of the monomer. For example, hyperbranched aromatic polycarbonates have been prepared by the polymerization of an A.sub.2 B monomer derived from 1,1,1-tris(4-hydroxyphenyl)ethane CH.sub.3 C(C.sub.6 H.sub.4 OH).sub.3, in which one of the three phenol groups was protected by a trialkylsiloxy group, i.e., --OSi(CH.sub.3).sub.3, in preparing the monomer, which was then removed prior to its polymerization.
Only relatively few hyperbranched polymers containing the silicon atom in their complex structure are known, and these materials are based on a hydrosilylation reaction of silanes and siloxanes containing vinyl and Si--H functionality, respectively. As a result, this particular type of hyperbranched polymer contains a carbosilane linkage, i.e., .tbd.Si--CH.sub.2 --.
On the other hand, and in contrast, the present invention is directed to a new type of hyperbranched polymer having a basic structure containing an .tbd.Si--O--C.tbd. linkage.